Efficacy of Zest, Resolve, and Harmony Tank Mixes Used Efficacy of Zest, Resolve, and Harmony Tank Mixes Used Sequentially in Irrigated Acetolactase Synthase (ALS)-Resistant Sequentially in Irrigated Acetolactase Synthase (ALS)-Resistant Grain Sorghum

Summary Palmer amaranth control was best when Cinch was applied preemergence (PRE) followed by Zest plus atrazine postemergence (POST) or when Cinch ATZ was applied early postemergence (EPOST) with Zest and atrazine. Most herbicides provided excellent crabgrass control. Shattercane control was excellent with all herbicides except Cinch ATZ applied PRE. Minor sorghum stunting was observed with some treatments three days after application, but sorghum had completely recovered within one week. Herbicide-treated grain sorghum yielded 48 to 93 bu/a more grain than untreated sorghum. Sorghum yields were best when Cinch or Cinch ATZ was applied PRE followed by Zest and atrazine POST, or when Cinch ATZ was applied with Zest and atrazine EPOST.


Introduction
Zest (nicosulfuron) and Resolve (rimsulfuron) are herbicides that have long been used in corn to control weedy sorghum species as well as other grasses.Using selections from weedy sorghum species that had developed resistance to the ALS mode of action, commercial sorghum hybrids have been developed.Although these compounds provide excellent control of weedy sorghum species they can be weak on many broadleaf weeds and some grassy species beyond a certain size.Harmony (thifensulfuron), another ALS herbicide long used for weed control in wheat, was also included.Therefore, it was the objective of this study to compare tank mixes of herbicides to augment the weed spectrum of Zest and Resolve.

Experimental Procedures
An experiment was conducted at the Kansas State University Southwest Research-Extension Center near Garden City, KS, to evaluate weed control and crop response with acetolactase-synthase (ALS) inhibiting herbicides Zest, Resolve, and Harmony in irrigated ALS-resistant grain sorghum.Atrazine and Cinch (S-metolachlor) were also included to augment weaknesses in these compounds.Herbicides were applied preemergence (PRE), early postemergence (EPOST), or PRE followed by postemergence (POST).The experimental area was overseeded with crabgrass and Rox Orange forage sorghum (to simulate shattercane) to supplement naturally occurring weed pressure prior to planting sorghum.Application, environmental, and weed information is shown in Table 1.A tractor-mounted, compressed-CO 2 sprayer delivering 20 GPA at 30 psi was used to apply all herbicides.Plot size was 10 × 35 feet, arranged in a randomized complete block design with four replicates.Soil was a Beeler silt loam with 2.4% organic matter and pH of 7.6.Visual weed control was determined on July 17 and August 30, 2017, which was 6 and 50 days after the POST treatment (DAPT), respectively.Grain yields were determined on November 1, 2017, by mechanically harvesting the center two rows of each plot and adjusting weights to 14% moisture.
Figure 5. Cinch 1.0 pt/a applied preemergence followed by Zest 0.67 oz/a plus Atrazine 24 oz/a plus crop oil concentrate 2% plus ammonium sulfate 2 lb/a applied postemergence, 3 days after postemergence application.

Figure 3 .
Figure 3. Resolve 0.25 oz/a plus Harmony SG 0.125 oz/a plus Atrazine 24 oz/a applied preemergence followed by Zest 0.67 oz/a plus Atrazine 24 oz/a plus crop oil concentrate 2% plus ammonium sulfate 2 lb/a applied postemergence, 3 days after postemergence application.

Table 1 .
Application information

Table 2 .
Efficacy of single and sequential herbicides in acetolactase synthase-resistant grain sorghum